Highly conjugated organic materials have been the focus of great research activity, chiefly due to their interesting electronic and optoelectronic properties. They have been investigated for use in a variety of applications, including field effect transistors (FETs), thin-film transistors (TFTs), organic light-emitting diodes (OLEDs), electro-optic (EO) applications, as conductive materials, as two photon mixing materials, as organic semiconductors, and as non-linear optical (NLO) materials. Highly conjugated organic materials may find utility in devices such as RFID tags, electroluminescent devices in flat panel displays, and in photovoltaic and sensor devices. Organic semiconductors may substantially reduce production costs as compared to inorganic materials such as silicon, as they can be deposited from solution, which can enable fast, large-area fabrication routes such as spin-coating, ink-jet printing, gravure printing, or transfer printing, to name a few.
The performance of an organic transistor can be evaluated by several parameters such as carrier mobility, current on/off ratio, threshold voltage, and/or on/off current magnitude. Materials such as pentacene, poly(thiophene), poly(thiophene-co-vinylene), poly(p-phenylene-co-vinylene) and oligo(3-hexylthiophene) have been studied for use in various electronic and optoelectronic applications. More recently, fused thiophene compounds have been found to have advantageous properties. For example, bisdithieno[3,2-b:2′,3′-d]thiophene (1, j=2) has been found to efficiently π-stack in the solid state, possesses high mobility (up to 0.05 cm2V·s), and has a high on/off ratio (up to 108). Oligomers and polymers of fused thiophenes, such as oligo- or poly(thieno[3,2-b]thiophene (2) and oligo- or poly(dithieno[3,2-b:2′-3′-d]thiophene) (1)
have also been suggested for use in electronic and optoelectronic devices, and have been shown to have acceptable conductivities and non-linear optical properties. However, unsubstituted fused thiophene-based materials tend to suffer from low solubility, marginal processability and oxidative instability. Thus, there remains a need for fused thiophene-based materials having improved solubility, processability and/or oxidative stability.
Applicant has described fused thiophene compounds and methods for making such compounds, for example, in U.S. Pat. Nos. 7,705,108; 7,714,098; 7,838,623; 7,893,191; 8,217,183; 8,278,346; 8,278,410; 8,349,998; 8,389,669; 8,487,114; 8,575,354; and 8,846,855, all of which are incorporated herein by reference in their entireties. However, methods for making such fused thiophene compounds have thus far suffered from various drawbacks, such as long reaction schemes, low yields, and/or high operating costs. Scale-up of existing processes for making fused thiophene compounds has been difficult to carry out in a cost-effective manner.
Accordingly, it would be advantageous to provide methods for producing fused thiophene compounds that utilize shorter reaction schemes, have improved yields, and/or are less complex and/or costly. Additionally, it would be advantageous to provide thiophene intermediate compounds that circumvent the need for multiple reaction steps for forming fused thiophene compounds. In various embodiments, fused thiophene compounds may be produced according to the methods herein using far fewer steps as compared to prior art methods and, thus, the disclosed methods may exhibit higher yields and/or faster production times. Methods for producing fused thiophene compounds disclosed herein may also be easier to scale up for commercial production.